Apartment Common Egress Stair

[SuperFlyBriBri]

We are working on a design for a building in New Jersey following the International Building Code.

The building is going to have 4 residential apartment units.

The first 2 units are on the first floor and have access from a front porch.

The second 2 units are on the second floor and have access from a common stair located in the rear of the design.

The question is if the 2 second floor units share a common stair up to the units, then does that stair need to have a riser height of 7 inches and a tread depth of 11 inches?

We have an interior stair in each of these second floor units that go up to the attic level and those have 8-1/4 inch risers and 10 inch treads because they are inside each of the R-2 dwelling units.

I did see an exception for Group U occupancies that are accessory to individual dwelling units in Group R-2 occupancies where under Group U there is Towers but does that include Stair Towers?

 

[TheCommish]

The exception in the 2015 IBC is for stairways is

 

[SuperFlyBriBri]

I see that mentions inside the R-2 Dwelling Unit but these would be outside the dwelling unit door as it would be a shared common stair for the 2 second floor units.

That is why I was unsure what the other mention of the Group U meant and if that could be applied as a Stair Tower or something?

 

[mtlogcabin]

7/11 for the common stair

 

[SuperFlyBriBri]

7/11 for the common stair

That is what we have in there because we could not find an exception for it.

But I find it odd that when we originally had 2 exterior doors and 2 individual sets of stairs inside the individual dwelling units, they can be 8-1/4 by 10 but now that we changed it to a shared stair for the same 2 units, it switches to become 7 and 11 sizing.

 

[mtlogcabin]

The stair shared by the 2 units becomes common means of egress exit stair outlined in 1009.3

 

[tbz]

As noted by MT the building is a R2 Use group under the IBC, the stair section for tread and riser is Sec: 1011.5 for NJ

Specifically, section 1011.5.2 Riser Height and tread depth which restricts the riser to a 7-in maximum and restricts the tread depth to an 11-in minimum.

Exception 3 under 1011.5.2, allows within each individual dwelling unit of an R-2, a stair serving only the interior of that dwelling unit, are allowed to use a 8.25-in maximum riser and a 9-inch minimum tread. Which correlates with the parameters within the adopted NJ-IRC for 1 and 2 family homes.

The oddity you talk about is that the Private stair flights have now become public space. Not Odd, as this is no different than the if you had 10 apartments being served by a common stair flight.

As Harold Samuel said "Location, Location, Location"

Link to NJ IBC Section 1011.5.2 (below)

https://codes.iccsafe.org/content/NJBC2018P2/chapter-10-means-of-egress#NJBC2018P2_Ch10_Sec1011.5

 

[SuperFlyBriBri]

As noted by MT the building is a R2 Use group under the IBC, the stair section for tread and riser is Sec: 1011.5 for NJ

Specifically, section 1011.5.2 Riser Height and tread depth which restricts the riser to a 7-in maximum and restricts the tread depth to an 11-in minimum.

Exception 3 under 1011.5.2, allows within each individual dwelling unit of an R-2, a stair serving only the interior of that dwelling unit, are allowed to use a 8.25-in maximum riser and a 9-inch minimum tread. Which correlates with the parameters within the adopted NJ-IRC for 1 and 2 family homes.

The oddity you talk about is that the Private stair flights have now become public space. Not Odd, as this is no different than the if you had 10 apartments being served by a common stair flight.

As Harold Samuel said "Location, Location, Location"

Link to NJ IBC Section 1011.5.2 (below)

https://codes.iccsafe.org/content/NJBC2018P2/chapter-10-means-of-egress#NJBC2018P2_Ch10_Sec1011.5

Thanks so much for the information. I agree it is an little bit of an oddity but it is what needs to be done and we figured that we would accommodate for such anyway just out of caution. Now it will just be a little easier to go up the steps with groceries. Haha. Thanks again for everything.